1.) Sewer Systems
Sewer systems provide for the collection and conveyance of sanitary sewage and stormwater runoff. In a modern “separate” sewer system, a private property such as a house usually has one internal plumbing system for collection and conveyance of sanitary waste and wastewater from plumbing fixtures throughout the home. These fixtures may include toilets, showers, bathtubs and lavatories; dishwashers and kitchen sinks; laundry and utility sinks, internal drains and other fixtures. These fixtures and the plumbing system draining them are connected to a sanitary sewer by a sanitary sewer lateral pipe. Properly designed and maintained sanitary sewer systems convey sanitary waste to wastewater treatment plants where pollutants are removed before discharging to surface waters (e.g., rivers, streams, lakes, estuaries and coastal areas) or groundwater.
A typical house may also have another, separate plumbing system for collection and conveyance of rain water (or “stormwater”) and snowmelt runoff from roofs and other impervious surfaces. Stormwater plumbing systems and drainage infrastructure such as gutters and downspouts may be connected to a separate storm sewer system via a storm sewer lateral pipe. Properly designed stormwater drainage and storm sewer systems collect and convey stormwater runoff away from roofs, roads and other impervious surfaces to reduce the likelihood of local flooding. Stormwater management policies vary and in some localities storm sewers discharge directly to surface waters; in other areas storm sewers may be designed to convey stormwater runoff to a stormwater management system.
Properly designed and maintained separate sewer systems are effective at protecting public health and the environment. Unfortunately defects and improper connections may be present in and among plumbing systems, sewer lateral pipes and sewer systems. One type of defect is known as “cross-connection”, an undesirable condition in which there is a leak or hydraulic connection between components of the sanitary and storm sewer systems. For example, one or more sanitary sewer lateral pipes may be improperly connected to a storm sewer. Alternatively, storm sewer lateral pipes or other stormwater drainage infrastructure may be improperly connected to a sanitary sewer system. Sanitary sewage disposed in a home with a cross-connected plumbing system may not be conveyed to a wastewater treatment plant and may contaminate a storm sewer system that is not designed for sanitary sewage. Contaminated stormwater and sanitary sewage may then be released into the environment, causing pollution of surface waters or groundwater aquifers. Sewer lateral pipe and sewer system defects can thus cause or contribute to bacterial contamination and impairment of water supply uses of surface water and groundwater and may also impair recreational uses of surface waters.
The improper connection of storm sewer lateral pipes or other stormwater drainage infrastructure to a sanitary sewer system is also problematic. Sanitary sewers are usually built with smaller hydraulic capacity than storm sewers. As stormwater flow takes up space within the sanitary sewer system, the capacity of the sanitary sewer system to convey sanitary waste decreases, potentially resulting in basement backups or sanitary sewer overflows. Even if the additional stormwater flow can be conveyed without overflowing, treatment costs for wastewater treatment plants can increase, as the facility will have to treat a greater amount of flow than if only sanitary waste is collected and conveyed to the treatment works.
2.) Sewer System Testing
Due to the potential for pollution and other problems that sewer system defects can cause, owners and operators of separate sewer systems such as municipalities and regional authorities may need to inspect and test sanitary and storm sewer lateral pipes to verify that they are connected to the proper sewers and free from defects. Periodic inspections of sewer systems, including privately owned sanitary and storm sewer lateral pipes, may be required as a condition of permits issued by a state or federal regulator to the operator of the sewer system. Furthermore, ordinances in some localities may require a certificate of sewer lateral inspection be obtained for real estate transactions. Sewer lateral pipes must be inspected in order to certify that sewer lateral pipes on the subject property are properly connected and in good condition before property can be transferred.
Inspection of separate storm and sanitary sewer lateral pipes may also be initiated by a sewer system owner or operator based on routine checks of storm sewers or complaints from the public. Investigations may be required when there is evidence of illicit dry weather flow or when other indicators of sanitary sewage contamination are observed in storm sewers or at storm sewer outfalls. Storm sewer outfalls are often located along banks of rivers and streams where stormwater may be discharged into surface waters. Owners and operators of separate sewer systems, such as municipalities and regional authorities may also need to inspect and test sanitary and storm sewer laterals concerning the presence of infiltration and inflow (I&I) into the sanitary sewer system.
3.) Dye Testing
One method of testing and tracing sewer connections known in the art is the introduction of a visible dye in the plumbing system or other access point along the lateral pipe and visual inspection of the flow in a downstream observation point in the sewer system—such as a manhole—for the presence or visual evidence of dye. The dye testing process is labor-intensive as it usually requires at least two persons. One person typically introduces the dye into the system under investigation while another person must be physically present at a downstream observation location to observe the dye. Each dye test consists of two distinct physically- and temporally-linked events—the introduction of the dye, and the observation of the dye thereafter. This feature of the dye testing method is disadvantageous, making it a time-consuming affair to sequentially test multiple fixtures within a property and impractical to conduct tests of multiple properties or locations within the same sewer system network simultaneously.
Due to the “time-of-travel”, or the amount of time necessary for the dye to be conveyed between the plumbing fixture or other introduction point and the downstream observation point, it may be necessary to wait several minutes to determine the result of a dye test. It may also be necessary to wait several minutes between multiple dye tests to allow dye to disperse and ensure the reliability and independence of each test result. It may also be necessary for the persons conducting the test to remain in contact with one another and keep accurate time records in order to record the outcome of the tests conducted. Due to the temporal nature of the test procedure and the need to remain in communication, the closest downstream manhole or access point is often used as the observation point for each dye test.
Selecting observation points physically close to the property or sewer system being tested necessitates opening multiple manholes when testing multiple properties along a street as the work progresses. Moving the work zone and opening additional manholes or other access points can be time consuming and labor-intensive, as manhole covers are often found to be jammed with paving materials and debris. Workers may incur the dangers of using striking, prying and lifting tools to open additional manholes. Ladders, wet conditions and sewer gases such as hydrogen sulfide and methane are also potential hazards for observers that may enter the confined space of a manhole to make observations for the presence of dye.
Another safety disadvantage of dye testing is that suitable observation points such as manholes are often located within roads or other areas subject to vehicle or foot traffic. Opening manholes to make observations for the visual evidence of dye thus often requires securing a safety zone around the manhole to prevent persons or objects from falling into the manhole. Furthermore, at any time when a person is required to occupy an observation position in a road or other location where vehicles are operated, there exists the danger of the worker being struck by a vehicle. Closing lanes or entire roads to safely accommodate dye testing observers can cause inconvenience for motorists and may impede emergency vehicles.
In addition to the safety and time-of-travel disadvantages of dye testing, the dilution of dye by base wastewater flow in sanitary sewers requires that a relatively large amount of dye be used in order to provide definitive visual evidence of the presence of dye. Environmental conditions such as bright daylight can cause large differences in contrast between the ambient outdoor environment and the sewer system being tested, which is typically much darker. Flashlights are often used to illuminate the sewer observation point, but on bright days it may be difficult to see the dye unless a relatively large quantity of dye is used. Although dyes used for sewer system testing are typically non-toxic, dyes are expensive and have other undesirable characteristics such as the potential for staining surfaces and the unintended or unanticipated observation of dye at other non-testing locations.
4.) Camera Inspection and Advanced Methods of Sewer Inspection
Camera inspection is another type of testing known in the art that is used to inspect plumbing systems, sewer lateral pipes and sanitary and storm sewers. A variety of models of cameras are available for use in video inspection of sewer system components, from simple “push” cameras to more elaborate motorized and robotic cameras. Cameras can provide visual evidence of many types of sewer system defects but the use of cameras requires a suitable insertion point and skilled person to operate the camera and interpret the display or review recorded video footage of the inspection. Cameras can be impeded by pipe geometry, various types of pipe defects, or obstructions caused by tree roots or other debris.
In addition to dye testing and camera inspection, there are many other methods known in the art for deploying robots, sensors and other electronic monitoring devices in flowing fluid applications, such as force water and sewer mains, gas and oil pipelines, and wellbores. Such devices may be tethered or untethered, self propelled or passive. For example “Smart pigs” are a class of devices that are used to perform maintenance, detect leaks and monitor data within pipelines. These advanced technologies tend to require specialized equipment and skilled operators and are currently prohibitively expensive for use in plumbing system and sewer lateral pipe investigations.
5.) Disadvantages of Current Sewer Inspection Methods
As the need to inspect and test sewer lateral connections grows with tightening environmental regulations and deterioration of older sewer systems, owners and operators of sewer systems may find themselves needing to test a large number of sewer connections over a large geographical service area. When performing tests of each individual property plumbing system or sewer lateral pipe within a large area under investigation, it would be desirable to be able to test multiple fixtures, plumbing systems and sewer lateral connections from multiple properties in an arbitrary sequence rather than performing one test at a time as is the case with dye testing and camera inspection. It is possible to use different colors of dye to marginally increase the number of fixtures that can be tested concurrently, but this approach is limited by the number of colors of available dye that can be discriminated by an observer and is still subject to the disadvantages described above in terms of sequential testing.
It would also be very desirable to be able to choose a single downstream monitoring location or small set of monitoring locations for the observation of test results. It also would be desirable for test results to be determined automatically by electronic means rather than by an active human observer and for test results to be transmitted in near-real time to a server by a telemetry system. Neither dye testing nor camera inspection can yield the type of test results that can be quickly and readily integrated into an automated information technology workflow.
6.) Electronic Tagging and Tracking
A variety of methods for tagging and subsequent identification of objects are known in the art and used extensively for tracking cargo, articles in trade, livestock and domestic animals. A common type of electronic identification tag well-known in the art is the radio frequency identification (RFID) passive integrated transponder (PIT) tag, or “RFID PIT tag”. A typical RFID PIT tag consists of a silicon computer chip, capacitor, and wound copper antenna enclosed in a biologically inert glass capsule. RFID PIT tags may be used with an RFID reader and antenna system, typically comprising an RFID PIT tag reader, antenna, datalogger, power supply, appurtenant wiring, and optionally, a telemetry system. The RFID reader and antenna system can be used to interrogate, or “read” RFID PIT tags within the effective reading range of the antenna. When a compatible RFID PIT tag comes within range, a current is induced in the RFID PIT tag by the antenna, and an identification sequence, or code, stored on the RFID PIT tag chip can be transmitted to and read by the reader. The identification sequence encoded in each tag can be used to uniquely identify each RFID PIT tag from a known database of tag identification codes. RFID PIT tags are used extensively for identification of domestic livestock and pets as well as hatchery and farm-raised fish. For example, hatchery-raised migratory fish tagged with RFID PIT tags may be released into the natural environment and then later identified when they are caught by fishermen or researchers. Tagged hatchery-raised fish may also be identified when they pass by RFID reader and antenna systems installed within natural and man-made waterways such as stream channels, fish ladders and other fish passage facilities.
The distance at which a given RFID PIT tag can be interrogated and read depends heavily on the size and type of antennas used in the RFID PIT tag and in the RFID reader and antenna system. Several types of antenna designs and deployment methods are used in the art for application of RFID technology for building access, inventory control, manufacturing, raising and processing of livestock; and tracking of fish and wildlife. Typical RFID reader and antenna systems used for building entry or identification of domestic animals may only be capable of interrogating and reading tags at a distance of a few centimeters. The more powerful specially designed RFID reader and antenna systems used in fish monitoring applications may be capable of interrogating and reading 12.2×2.1 mm RFID PIT tags embedded in the body cavity of swimming fish with detection distances of 50 cm or more.
7.) Fluid Flow Measurement by Float or Entrained Body
The flow of water or other fluid movement in a confined pipe or open channel may be measured by tracking and recording the movement of a floating or suspended object (drogue, or body) floating within or entrained by the flowing fluid to be measured over a given distance. Numerous methods are known in the art for the measurement of velocity or discharge of a flowing fluid by tracking objects within the flowing fluid. Floating or neutrally buoyant objects (bodies) such as oranges or specially weighted floating rods have been used to measure flow in rivers. Positively buoyant objects are generally preferred for flow measurement due to the propensity of denser objects to become trapped or drag on the bottom of the channel to be measured. When a floating or entrained object is used for flow measurement a coefficient or adjustment factor may be used to compensate for the fact that the fluid flowing nearer the surface will be flowing at a higher velocity than the fluid nearer the bottom or sides of the channel. The use of floating and entrained object tracking methods is relatively uncommon, however, due to the availability of more advanced methods known in the art such as acoustic Doppler velocimetry.
8.) Conclusion
From the preceding information, it is clear that there are significant disadvantages to existing methods for testing plumbing systems, sewer lateral pipes and sewer systems under some test conditions and for certain testing objectives.